The present invention relates to a color display device used in televisions or computers for image display, and in particular a plasma display panel having phosphor films, a method of manufacturing therefor, and a phosphor ink applying device for use when applying the phosphor film.
Among various types of color display devices used for displaying images on computers or televisions, Plasma Display Panels (PDPs) have become a focus of attention as color display devices that enable large-size, slimline panels to be produced.
PDPs display in full color according to an additive process of the so-called three primary colors (red, green, and blue). In order to perform this full color display, a PDP is composed of stripe-shaped barrier ribs interposed between a front panel and a back panel, and a phosphor film between each barrier rib that emits light in one of the colors red (R), green (G), and blue (B). Images are displayed by phosphor particles which form the phosphor film being excited by ultra violet rays generated in discharge cells of the PDP. This produces visible light in the colors.
Japanese Laid Open Patent Application H10-27543 discloses a method for forming such phosphor film. In this method, a phosphor ink applying device is used, and ink is continuously discharged from a plurality of nozzle apertures which are provided in a row with a distance therebetween of three times the pitch between each barrier rib. By moving the nozzle over the PDP platform, a plurality of lines of phosphor are applied simultaneously to the grooves between the barrier ribs.
According to this method, phosphor ink is continuously applied to the grooves, resulting in phosphor particles being formed evenly in the lines. Furthermore, applying a plurality of lines simultaneously means that not only can variations between the amount of ink applied to each line be controlled, but also that the amount of time required to apply the phosphor is reduced and work efficiency is improved.
In recent years techniques have been developed to improve brightness of PDPs by making the barrier ribs meandering rather than straight lines, or by providing auxiliary barrier ribs at predetermined intervals in the grooves between the barrier ribs (for example, see Japanese Laid-Open Patent Application H10-321148). Here, the auxiliary barrier ribs are lower than the barrier ribs.
FIG. 9 is a perspective view of barrier ribs and auxiliary barrier ribs. As shown in this figure, barrier ribs 1a, 1b, and 1c are formed in striped shapes with intervals therebetween, and auxiliary barrier ribs 2a and 2b, and 2c and 2d are formed in the grooves in the intervals between the barrier ribs 1a and 1b, and 1b and 1c respectively. Discharge spaces 3a and 3b are formed in the spaces between each barrier rib and auxiliary barrier rib.
Taking the discharge space 3a as an example, phosphor film is formed on side walls 4 and 5 (the side wall 5 is not visible in the diagram) of the auxiliary barrier ribs 2a and 2b, respectively. As a result, the light emitting area is larger than when auxiliary barrier ribs are not provided, because of the extra area of the side walls, meaning that the brightness of the PDP is improved.
However, when phosphor ink is applied to a back panel which has such auxiliary barrier ribs using the conventional phosphor ink application described earlier, the phosphor ink discharged through the nozzle apertures is applied successively parallel to the barrier ribs by moving the PDP in relation to the phosphor ink applying device. However, this gives rise to a problem in which, for instance, ink applied to the top portion 6 of the auxiliary barrier rib 2a flows over the barrier ribs 1a and 1b into the adjacent discharge spaces which emit light of a different color, causing the colors to mix. This problem can also occur in portions between barrier ribs where the gap is narrow in back panels which have meandering barrier ribs. A PDP cannot perform full color display if such color mixing occurs.
In view of the above-described problem, the object of the present invention is to provide a phosphor ink applying device and a method for manufacturing a PDP for applying phosphor ink in a plurality of lines to an intricately-shaped surface of a back panel of a PDP while preventing phosphor colors mixing, and a PDP formed using the phosphor ink applying device and the method of manufacturing.
In order to achieve the object, the present invention is a phosphor ink applying device for applying phosphor ink in a plurality of parallel line-shapes to a surface of a work according to movement in relation to the work, including a plurality of tanks for storing fed-in phosphor ink, a plurality of nozzle members, each nozzle member having one nozzle aperture which is linked to a storage chamber of one of the tanks, a moving unit for moving the nozzle members in relation to the surface, a pressuring unit for applying pressure to the phosphor ink stored in the tanks so as to discharge the phosphor ink through the nozzle apertures, and a control unit for individually controlling a discharge quantity of phosphor ink discharged through each nozzle aperture, according to a shape of a portion of the surface to which the phosphor ink is to be applied.
According to this structure the discharge quantity of phosphor ink which each nozzle aperture discharges can be controlled individually, even when the portion to which phosphor ink is to be applied is intricately-shaped, therefore phosphor ink can be applied in a plurality of line-shapes simultaneously. This means that when phosphor ink is applied to a substrate of a plasma display panel which has auxiliary barrier ribs, the amount of ink which is applied to the top of the auxiliary barrier ribs can be controlled to be less than that applied to other places. As a result, color mixing due to phosphor ink flowing over barrier ribs can be prevented. Furthermore, the discharge quantity from each nozzle can be controlled, so phosphor ink is only applied where necessary, even if the positions of the nozzles are misaligned in the movement direction relative to the surface. In other words, there is much freedom in the positioning of the nozzles.
Furthermore, if each nozzle member includes a discharge quantity varying unit for varying the discharge quantity through each nozzle aperture, and the control unit controls the discharge quantity of the phosphor ink through each nozzle aperture according to the shape of the portion of the surface to which the phosphor ink is to be applied by driving each discharge quantity varying unit individually, an appropriate quantity of phosphor ink can be applied where necessary even to an intricately-shaped surface.
Furthermore, the pressuring unit may include an applied pressure varying unit for each tank for varying the pressure applied to the phosphor ink, and the control unit may control the discharge quantity of the phosphor ink through each nozzle aperture according to the shape of the portion of the surface to which the phosphor ink is to be applied, by driving each applied pressure varying unit individually.
Furthermore, the phosphor ink applying device of the present invention is for applying phosphor ink in a plurality of parallel line-shapes to a surface of a work, including one or more tanks for storing fed-in phosphor ink, a plurality of nozzle members, each nozzle member having one nozzle aperture linked to a storage chamber of one of the tanks, a moving unit for moving the nozzle members in relation to the surface, a pressuring unit for applying pressure to the phosphor ink stored in the tanks so as to discharge the phosphor ink through the nozzle apertures, a discharge quantity varying unit being provided for each nozzle aperture and varying a discharge quantity of phosphor ink to which pressure is applied, and the control unit controlling the discharge quantity of the phosphor ink through each nozzle aperture according to the shape of the portion of the surface to which the phosphor ink is to be applied, by driving each discharge quantity varying unit individually.
According to this structure, when phosphor ink is applied to a substrate of a plasma display panel in the same manner as described above, mixing of colors can be prevented. In addition, a plurality of nozzle apertures are provided for one tank, meaning that the number of tanks can be reduced and the phosphor ink applying apparatus can be made compactly.
Here, if the nozzles are positioned misaligned in the direction of relative movement, phosphor ink can be applied with the distance between adjacent line-shaped phosphor ink shortened.
Furthermore, the discharge quantity varying unit can be used as a flow path resistance unit for varying the discharge quantity by varying the flow path resistance of the phosphor ink through the nozzles. Specifically, a valve can be used as the discharge quantity varying unit.
A specific example of the object to which phosphor ink is applied is a substrate for a plasma display panel.
Furthermore, the moving unit includes a slideable table for carrying a substrate of a plasma display panel that has the barrier ribs provided in a row, and each nozzle is provided above the grooves formed between the barrier ribs of the substrate for the plasma display panel carried by the moving table. Therefore, phosphor ink can be applied in the grooves of the substrate carried by the table, in parallel, in accordance with the movement of the moving table.
Furthermore, the method of the present invention for manufacturing a plasma display panel, is a method including an ink application process for applying to a substrate for a plasma display panel which has (a) a plurality of first barrier ribs provided so grooves are formed therebetween, and (b) second barrier ribs which are provided at a predetermined interval in the grooves and which have a height lower than the first barrier ribs, phosphor ink in a line shape parallel to the first barrier ribs in each groove successively, and including, in the ink application process, the quantity of phosphor ink applied to walls of the second barrier ribs being less that the quantity of phosphor ink applied to areas between the second barrier ribs. According to this structure, flow of the phosphor ink applied to the gaps between the second barrier ribs over the first barrier ribs can be suppressed, meaning that color mixing on the substrate can be suppressed.
Furthermore, the plasma display panel of the present invention is formed with a substrate which has (a) a plurality of first barrier ribs provided so grooves are formed therebetween, (b) second barrier ribs which are provided at a predetermined interval in the grooves and which have a height lower than the first barrier ribs, and (c) line-shaped phosphor film parallel to the first barrier ribs formed in each groove successively, and the phosphor film is applied more thinly to a top portion of the second barrier ribs than to the areas therebetween. Color mixing during driving display can be suppressed in such a plasma display panel.